If you have a `has_one through` assocation where the `through` has a
`belongs_to` the foreign key won't be `id` for the joins. This change
ensures we use the correct foreign key when querying with disable joins
turned off. Prior to this change the call to `project.lead_developer`
would return `nil` if `disable_joins` was set.

Project has one lead developer through firm. Project also belongs to
firm. So when we call `project.lead_developer` it needs to find the
lead developer through the firm. In these cases we don't want to read
the owners id, we want to read the attribute that will give us the
value of the first chain item's `join_foreign_key`.